Vehicle air conditioning (AC) systems may include AC compressors that are not electrically powered. In particular, they may be powered by a front end accessory drive (FEAD) of an engine, and may be connected to the FRAD through a system of belts and pulleys. When operated, the AC compressor pressurizes refrigerant flowing there-through based on cabin climate control demands of a vehicle customer. This enables the compressor to meet the desired cabin temperature set by the vehicle customer.
One issue with FEAD driven compressors is that the compressor does not work when the engine is turned off. As a result, while an engine is shutdown, there may be a rise in refrigerant temperature and a resulting increase in AC evaporator temperature. For a given blower speed setting, the increased evaporator temperature can generate an unpleasant musty odor which transfers to the passenger cabin and results in a drop in cabin air quality.
Various approaches have been developed to improve cabin air quality. One example approach is shown by Matsui et al. in JP2013203354. Therein, during an engine idle-stop, wherein an engine is shutdown responsive to a drop in torque demand, an AC system is moved to a fan only mode (from a heating or cooling mode) and a fragrance is delivered into a vehicle interior vehicle a fragrance delivery unit as a function of cabin air temperature. In particular, fragrance delivery is increased when cabin air temperature increases.
However, the inventors herein have recognized potential issues with such systems. As one example, the approach may cause a drop in the fuel savings, reduction in exhaust emissions, and reduction in noise that are achieved through idle-stop operations. In particular, the duration of the engine idle-stop may be limited by an evaporator temperature limit. In order to avoid a significant increase in the evaporator temperature, and the resultant humidity that drives the musty air, the engine may have to be restart ahead of high temperatures being reached in order to ensure that the customer does not get the musty smell. As a result, the engine-off time is reduced, which limits the opportunity of fuel economy and emission savings.
In one example, the issues described above may be addressed by a method comprising: delaying an engine restart from idle-stop by dispensing a fragrance through an air vent into a vehicle cabin. In this way, an engine idle-stop may be prolonged.
As an example, during an engine idle-stop, a fragrance dispensing device integrated into a vehicle heating ventilation and air conditioning (HVAC) system may be operated to extend the duration of the idle-stop. For example, an output of the fragrance dispensing device may be adjusted as a function of an odor and/or air quality sensor coupled to the interior of the vehicle to measure the humidity/musty level that is reaching the passenger cabin. If the sensor measurement exceeds a calibratable threshold during the idle-stop, diffusion rate of the fragrance may be increased to freshen up the air quality at the vent. The diffusion rate may be adaptively adjusted to the number of the passengers in the vehicle (such as may be detected via occupancy sensors). Further still, the diffusion rate can be adjusted as a function of the predicted duration of idle-stop, ambient temperature, and ambient humidity.
In this way, a duration of vehicle idle-stop can be prolonged while providing an improved air quality in a vehicle cabin. By reducing the need to restart a vehicle engine to avoid a musty odor, benefits related to engine idle-stop operations, such as reduced fuel economy and exhaust emissions, are extended over a longer portion of a vehicle drive cycle.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.